Vaccine ‘hotspots’ multiply exposure

Public health officials have long known that the United States has pockets of vulnerability where the risk of measles and other vaccine-preventable childhood diseases is higher because parents hesitate or refuse to get their children immunized.

Eighteen states allow parents to opt their children out of school immunization requirements for nonmedical reasons, with exemptions for religious or philosophical beliefs.

And in two-thirds of those states, a comprehensive new analysis finds a rising number of kindergartners who have not been vaccinated.

In a report published Tuesday in PLOS Medicine, researchers from several Texas academic centers tracked the increasing number of kids with exemptions in all 18 states from the 2009-10 to 2016-17 school years.

They characterized many rural counties, as well as urban areas, as “hotspots” because their high exemption rate puts them at risk for epidemics of measles, whooping cough and other pediatric infectious diseases.

Idaho has eight of the top 10 counties with the highest exemption rates, the study found. In Camas County in southern Idaho, nearly 27 percent of the kindergarten population opted out of childhood vaccinations in the 2016-17 school year, according to the study.

Generally, the 10 counties with the highest exemption rates have fewer than 50,000 people and are located in states’ rural areas.

But researchers also ranked urban areas. Among counties where more than 400 kindergartners received nonmedical exemptions in 2016-17, the 15 metropolitan locations with the most exemptions were Seattle and Spokane in Washington; Portland, Ore.; Phoenix; Salt Lake City and Provo, Utah; Houston, Fort Worth, Austin and Plano, Texas; Detroit, Troy and Warren, Mich.; Kansas City, Mo.; and Pittsburgh. “We were able to identify some scary trends that were happening,” said Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine and one of the study authors.

Federal health officials have said immunization rates haven’t changed much at national and state levels, Hotez said. But the new county-level data show conditions similar to those that resulted in recent measles outbreaks in California and Minnesota, he said. In many of those areas, anti-vaccination proponents have mounted aggressive and well-funded efforts.

Hotez said he didn’t know what factors were behind the high exemption rates in some of the rural places; researchers are hoping to conduct a follow-up study on social and demographic factors.

But the findings, he said, should prompt health agencies such as the Centers for Disease Control and Prevention to investigate.